Buried Moire supercells through SrTiO₃ nanolayer relaxation

The interface of complex oxide heterostructures sets the stage for various electronic and magnetic phenomena. Many of these collective effects originate from the precise structural arrangement at the interface that in turn governs local spin- and charge interactions. Currently, interfacial straining, so the naturally evolving compressive or tensile strain by mismatch of the neighboring lattices, is the most common route towards engineering collective material properties -- yet, significant progress might require exploration of entirely new approaches towards interface correlations. In this work, we turn the page by looking at the interface of a perfectly relaxed, unstrained heterostructure, where we identify a highly ordered Moire lattice at an inherently disordered SrTiO$_3$ (STO) - LSAT interface. Using high-resolution reciprocal space mapping via synchrotron based X-Ray diffraction, we find long-ranged ordered supercells of 106/107 unit cells of STO/LSAT, caused by lattice relaxation through high-temperature annealing. Model calculations confirm the experimentally observed scattering phenomena, showing that cross-interfacial bonding is locally different at the Moire-overlap points. Notably, the presence of such super-ordered structures in the family of 2D electron gas systems sets the ideal conditions for Moire-motif tuned plasmonic responses and ferroelectric super-crystallinity and opens up the possibility to novel interface functionalities in these simple perovskites.